The energy of the spark resulting from the collapse of the magnetic field of an automotive ignition coil is a function of one half LI.sup.2 where L is the inductance of the primary winding of the coil and I is the current. As the inductance for a given primary winding is a fixed value, then the energy which can be stored in the coil is directly proportional to the square of the current.
In the conventional automotive ignition system the flow of current into the ignition coil is controlled by mechanically actuated breaker points. It is very important in this type of system that the points be adjusted for proper dwell. Dwell is the number of degrees of crankshaft rotation during which the points are closed and current is allowed to flow into the coil. In the conventional ignition system, dwell will vary depending upon the number of cylinders in the engine. However, in the conventional automotive system, the dwell ratio is commonly set at two to one. Dwell ratio is the ratio of the time that the current flows into the ignition coil to the time that current does not flow into the ignition coil. In other words the dwell ratio is the ratio of the charging interval to the noncharging interval. For the typical breaker point system, the dwell ratio is the ratio of the period of time that the points are closed to the period they are open.
Because the energy of the ignition spark increases with increased current flow to the coil, many attempts have been made to increase the dwell ratio. One of these prior art devices includes two sets of points arranged so as to increase the dwell ratio. Other prior art systems use electronic means to increase the dwell ratio. The electronic systems typically employ a resistance-capacitor time constant circuit to activate a solid state switch device which, after a fixed predetermined period of time, initiates the flow of current into the coil. With this electronic system, current flow into the coil is initiated long before the breaker points close. This system does increase the dwell ratio at lower engine speeds. Unfortunately, however, the fixed predetermined period of time does not maintain this advantageous dwell ratio as engine speeds increase. Rather, the dwell ratio is reduced at higher engine speeds. In fact, at higher engine speeds the dwell ratio may be reduced to approximately the two to one ratio of the conventional automotive ignition system. Thus, at higher engine speeds where a high dwell ratio is needed most, the dwell ratio is low.